The field of the invention is switches, and more particularly multi-band switches for wireless transmission and reception as fabricated on a single semiconductor chip.
Conventional switch devices operate to control the path on which a signal travels. In general, there are two basic types of switch devices in use: electromechanical and solid state. Solid state switches use some kind of semiconductor device for the switching process, which can be diodes, field effect transistors or bipolar transistors. In general, diode switches have a lower insertion loss, while switches comprised of transistors are faster. Field effect transistors (FETs) have been employed in the switching of high frequency signals, such as radio frequencies (RF).
A FET switch is in an OFF status (high impedance) until a control voltage of a predetermined magnitude (saturation voltage) is applied to its gate. When the saturation voltage is applied to the gate, the FET switches to an ON status in which its current path between its source and drain exhibits very low resistance.
While a theoretical FET switch would provide no output until the saturation voltage is applied to the gate, at which point a predefined output would be provided to the drain, in practice FETs leak current prior to the application of the saturation voltage. Further, after the control gate voltage is reached and the switch is in operation, harmonics appear in the output voltage. Circuit designers seek to sharpen the point at which FETs turn on and seek to minimize output voltage harmonics. At the same time, integrated circuit designers seek to minimize on-chip real estate wherever possible, while at the same time pursuing lower control voltages. Designers of signal switches also attempt to minimize the impedance insertion loss in the signal path.
In conventional wireless switching practice (e.g. wireless LAN, Bluetooth, CDMA, TDMA, GSM, W-CDMA and the like) there has developed a need to both transmit data outward on an antenna and to receive data inward on an antenna in wireless fashion. Heretofore these tasks have been performed using different transmitter and receiver chips. It would be technically advantageous to combine these functions on a single-die integrated circuit which, however, does not unduly suffer from having its receiver ports being unduly loaded with capacitance due to the coexistence of on-chip transmitter switching circuits, and vice versa.